Blast resistant water door



March 10, 1964 H. L. BRODE BLAST RESISTANT WATER DOOR Filed July 11, 1961 INVENTOR.

HAROLD L. BRO E BY 41/0. OK

ATToRNEYs United States Patent 3,123,977 BLAST RESISTANT WATER DOOR Harold L. Erode, Santa Monica, Caiif., assiguor to the United States at America as represented by the Secretary of the Air Force Filed Juiy 131', 1961, Ser. No. 123,323 1 Claim. (Q1. 61--.5)

Underground installations must have openings to the outside world for normal and probably frequent daily access. Many such underground installations have a military mission which would make them attractive targets and subject to specific attack. For this reason a great deal of thought and consideration must be directed to the location and length of tunnels to such underground installations, the outside opening to such tunnels in regard to terrain features and means for protection against a multimegaton explosion near the entrance to such tunnels.

For example, such an explosion near the tunnel entrance may produce a blast wave in the order of 1000 pounds per square inch. Consideration must be given to the problem of preventing damaging pressures from reaching the underground installation where harm would result to personnel and sensitive equipment. A blast wave of given finite intensity will not travel through a tunnel at initial intensity, the intensity being constantly reduced by decay and by attenuation within the tunnel itself. It has been calculated that a blast wave of 1000 pounds per square inch initial intensity at the opening of a 15 foot tunnel would be completely dissipated in a tunnel of about one and one-half mile length or slightly less.

To reduce the required length of tunnels and to assure protection from blast pressure, blast doors or other shock attenuating or absorbing devices are advisable. A door at the tunnel entrance or portal is unattractive for at least two reasons: (1) It must withstand the highest expected portal overpressure whereas a door somewhat back of the opening need withstand considerably less and (2) If on attack the tunnel portal lies in the bomb crater, the door itself will be destroyed before fulfilling its mission and the tunnel will be exposed to the high initial blast pressure.

Blast doors placed in the tunnel well back from the portal would be protected from possible cratering action, however, such doors would be subjected to tremendous peak reflection overpressures which are considerably in excess of the initial blast pressure. On normal reflection from steel blast doors, a 1000 p.s.i. shock jumps to 8000 p.s.i. and a modest 100 p.s.i. shock becomes 480 p.s.i. on reflection. It is obvious that a simple door blocking a tunnel must face reflection pressures at least several times greater than initial blast pressures.

Any mechanical closure system has the disadvantages of possible jamming or malfunction after an explosion, of requiring detailed or awkward procedures for normal opening and closing and of requiring considerable power for the movement of large masses. The massiveness of a metallic closure system is essential for the absorption of high impulses, but leads to a cumbersome moving parts system with slow reactions and considerable power requirements.

Various other schemes for the dissipation of blast impulses are known, all of which, while offering some relief, also have inherent disadvantages. Examples of such schemes include the turning of corners within the tunnels, side branches in the main tunnel leading off in more or less opposite directions from the incoming blast, expansion into large chambers or reverberating around in a system of baffles and chambers not unlike a system employed for sound attenuation.

One object of this invention is to provide a simple and effective blast barrier which is jamb proof.

3,123,977 Patented Mar. 10, 1964 Another object of the invention is to provide a blast barrier having a minimum number of moving parts and utilizing a readily available fluid as the sealing means.

Still another object of this invention is to provide a barrier or blast door which can be easily closed without resort to an outside power source and which requires no detailed instruction or procedure for its operation.

Additional objects, advantages and features of the invention reside in the construction, arrangement and combination of parts involved in the embodiment of this invention as will appear from the following description and accompanying schematic drawing in which the figure is a vertical sectional view of the invention.

Referring to the drawing an underground passageway or tunnel 10 communicates between an outside entrance or portal 12 and an underground installation 14. The tunnel may be of any convenient size and cross-section, regular or irregular, without effect upon this invention. Within tunnel it) at some distance downstream from portal 12 where an initial blast pressure of 1000 p.s.i. would decay to say about 150 p.s.i., the floor of the tunnel is sloped to form a gravity fluid or water trap 16 as shown on the drawing. The fluid trap is of such depth that when filled to a predetermined depth with fluid, the elevation of the extremities or ends 1811 and 18b of the body of fluid 18 is substantially above the elevation of the ceiling Ma of tunnel it) at the low point of the fluid trap. It is thus seen that the body of fluid will completely seal the tunnel passage and provide a blast barrier or door.

An underground storage reservoir 20 of ample capacity to store at least suflicient fluid to fill the fluid trap is at any convenient elevation above the tunnel to permit the fluid to flow by gravity through passage 21 and valve 22 into the fluid trap 16. For convenience and simplicity valve 22 is shown to be hand-operated; however, if desired a motor operated and remotely controlled valve may be used. Likewise, reservoir 20 could be placed at any convenient location without regard to elevation and the fluid pumped into the fluid trap 16 by pumping means well known to the art.

Sump reservoir 24 is at some convenient elevation below the floor elevation at the low point in the fluid trap and is used as a sump or reservoir for the fluid which may be drained from the fluid trap through passage 26 and valve 28. Valve 28 for convenience and simplicity is shown to be hand operated; however, if desired a motor operated and remotely controlled valve may be substituted. Self-priming pump 30 which may be either of the centrifugal or positive displacement type returns the fluid from reservoir 24 to reservoir 20. The fluid flows from reservoir 24- into pump 39 through inlet pipe 32 and from pump 30 to reservoir 29 through discharge pipe 34.

The fluid trap 16 may be constructed to any desired length to thereby establish the maximum amount of fluid which may be trapped. The amount of necessary fluid may be determined from the anticipated blast pressure reaching end 18a of the trapped body of fluid 18. It is desired that the body of fluid have enough mass to resist acceleration from the blast impact in order that it not be driven downstream in the tunnel. In the example previously used where the initial blast pressure is anticipated to be 1000 p.s.i. and the fluid trap is located within the tunnel at a point where such blast pressure would have decayed to 150 p.s.i., and using water as the fluid, a body of water linear feet in length would suflice. The small amount of motion imparted to such a body of water could be easily dissipated by splash barriers or diverted down a short side tunnel into a pit, or allowed to fall through a grating in the tunnel floor and drain into reservoir 24 or be otherwise disposed. When the blast strikes the water, the pressure is transmitted through the water 3 but is not felt in the farther down the tunnel because of the impedence mismatch.

In operation, when it is desired to seal the tunnel with a water door, valve is closed to prevent draining the water trap and valve 22 is opened until the proper amount of water has flowed into the water trap after which valve 22 is closed. After the all clear signal has been given, the tunnel is drained by opening valve 28.

It is obvious that on certain installations with an adequate supply of fresh water, water may be taken directly from a water main and water drained from the water trap may be discarded.

While a preferred form of the invention has been shown and described, various modifications and substitutions of equivalents will occur to those skilled in the art after a study of the foregoing disclosure. However, the disclosure should be taken in an illustrative rather than in a limiting sense; and it is the desire and intent to reserve all modifications within the scope of the claim.

I claim:

In an underground tunnel and the like connecting an underground installation to the outside, a blast barrier comprising: a gravity water trap within said tunnel, storage reservoir, said storage reservoir being underground and at an elevation greater than said tunnel, water stored within said storage reservoir, valve controlling the gravity flow of said water from said storage reservoir into said gravity water trap to a predetermined level higher than the tunnel ceiling at the low point of the water trap, passage for draining said water from said gravity water trap through an openable valve into a sump reservoir located at an elevation below the low point in said gravity water trap, and means for returning said drained water from said sump reservoir to said storage reservoir.

References Cited in the file of this patent UNITED STATES PATENTS 634,554 Gartz Oct. 10, 1899 2,699,117 La Prairie Jan. 11, 1955 2,880,593 Johnson et al. Apr. 7, 1959 FOREIGN PATENTS 145,052 Germany Oct. 31, 1903 

